1. Field of the Invention
This invention relates generally to computer expansion buses and, more specifically, to PCMCIA (Personal Computer Memory Card International Association) bus equipped computers which require insertion and removal of expansion cards to be accomplished while the computer is in operation.
2. Description of the Prior Art
Buses for notebook and portable computers are needed which allow the simple connection and disconnection of peripheral equipment to ease portability and reduce power consumption. One such bus is the PCMCIA bus. Using this bus, peripheral and memory expansion cards (hereinafter cards) can be inserted and removed during system operation without disturbing the operation of the system. Software and BIOS support enable detection and initialization of the peripheral or expansion card so that the peripheral or expansion card can be used without shutting down or restarting the system. Insertion of a card while the system is operational is known as hot docking of a card.
PCMCIA buses have traditionally provided for insertion and removal of cards during system operation by electrically isolating the primary bus signals of the computer from the bus signals present on the on card connectors. This is usually accomplished by buffers disposed between the system primary bus and each peripheral bus connector and separate buffers are used for each bus connector and one for other non-removable system resources that require buffers such as a Flash ROM and BIOS ROM (hereinafter ROM). The separate buffers are required so that on insertion or removal of a card, the operation of other cards or ROM is not disturbed and their states are not corrupted. The partial bus connection, which occurs on insertion or removal of a card, causes the components on the card to enter undesired states and in these states, they may drive their signals onto the bus, causing improper operation of the system. The separate buffers traditionally provided between the bus connectors and other peripherals and system components ensure that this improper operational state does not affect system operation or operation of other peripherals by isolating the signals on that card from the rest of the system. When a card is inserted, card detect signals, which are located on pins which are physically shorter than the bus signal pins, allow the system to produce a card detected signal which is used to enable the bus buffer.
Also in the prior art, the card detect pins on the PCMCIA connector have been used to direct the PCMCIA controller to disable power to the PCMCIA connector. This enhances the possibility of data corruption, and therefore the need for separate buffers, as the supply voltage on the PCMCIA card may drop out of operating range before the bus signal pins are disconnected.
The need for these buffers presents several disadvantages. They consume area on the peripheral bus controllers and they increase the overall pin count since the bus connections, as well as the ROM and FLASH connections, require separate pins. Thus, they raise the cost and complexity of computers that use these buses.